A major hurdle in brain-machine interfaces (BMI) is the lack of an implantable neural interface system that remains viable for a substantial fraction of a primate lifetime. Recently, sub-mm implantable, wireless electromagnetic (EM) neural interfaces have been demonstrated in an effort to extend system longevity. However, EM systems do not scale down in size well due to the severe inefficiency of coupling radio waves at mm and sub-mm scales. We propose an alternative wireless power and data telemetry scheme using distributed, ultrasonic backscattering systems to record high frequency (~kHz) neural activity. Such systems will require two fundamental technology innovations: 1) thousands of 10 – 100 um scale, free-floating, independent sensor nodes, or neural dust, that detect and report local extracellular electrophysiological data via ultrasonic backscattering, and 2) a sub-cranial ultrasonic interrogator that establishes power and communication links with the neural dust. To test the feasibility of this approach, we performed the first in-vivo experiments in the rat model, where we were able to recover mV-level action potential signals from the peripheral nerves. Further miniaturization of implantable interface based on ultrasound would pave the way for both truly chronic BMI and massive scaling in the number of neural recordings from the nervous system.